Modern turbines often operate at extremely high temperatures. The effect of temperature on the turbine blades, stator vanes and surrounding components can be detrimental to the efficient operation of the turbine and can, in extreme circumstances, lead to distortion and possible failure of such components. In order to overcome this risk, high temperature turbines may include hollow blades or vanes incorporating so-called jumper tubes to aid the cooling and sealing flow systems by minimising the heat pickup within these flows, which can be especially critical for a disc region of the aerofoil assembly.
These so-called jumper tubes are hollow tubes that run radially within the blades or vanes. Air is forced into and along these tubes. The design intent is to minimise the heat pick up of the flow as it passes through the tube. To prevent heat transfer from the jumper tube to the aerofoil the jumper tube is arranged with an air gap in respect to an aerofoil cavity wall. The air gap creates an insulating layer of relatively low thermal conductivity. Heat transfer across the air gap is largely by radiation.
By operation with high flow rates through the jumper tube this design works very well. However, problems arise for low flow rates through the jumper tube causing high heat pickup of the cooling stream. When this temperature rise becomes excessive, the integrity of the disc cooling system can be significantly affected, and an excess cooling is required to compensate.
It is a first objective of the present invention to provide a method for cooling at least a part, especially a disc region, of a turbine assembly with a cooling medium with which the above-mentioned shortcomings can be mitigated, and especially a more aerodynamic efficient aerofoil and gas turbine component is facilitated.
It is a second objective of the invention to provide an advantageous aerofoil-shaped turbine assembly such as a turbine rotor blade and a stator vane. A third objective of the invention is to provide an advantageous jumper tube used in such an assembly for cooling purposes.